Abstract IL-17A (IL-17) is a pro-inflammatory cytokine that is secreted primarily by lymphoid cells, including CD4+ Th17 cells, ?? T cells, natural T cells and innate lymphoid cells (ILC17), and is induced following fungal and bacterial infections, and in autoimmune disease. IL-17 activates receptors on endothelial and epithelial cells to produce CXC chemokines such as IL-8, which is chemotactic for neutrophils. There are also multiple reports that neutrophils produce IL-17 in infected and autoimmune individuals, and in murine models of infection and autoimmunity. However, a recent study showed that the IL-17 locus is not in an active status in human neutrophils (Cassatella 2018). We reported Il17a gene expression in neutrophils during Aspergillus infections, and in neutrophils from fungal infected patients and healthy individuals in India, but not in healthy individuals in the USA. We therefore suggest that long-term exposure to fungal spores is a potential mediator of epigenetic modifications in neutrophils that results in accessibility of the IL-17 gene locus. We therefore propose to examine IL-17 promoter accessibility and histone modifications in this region using ATAC sequencing and ChIP-PCR in neutrophils from fungal infected patients in India compared with healthy individuals in the USA. Rheumatoid arthritis patients also produce IL-17 (Ortiz-Navarrete, 2019), indicating that chronic inflammation also leads to epigenetic modifications in the Il17a locus. Under conditions where the IL-17 locus is accessible, we will identify which transcription factors bind to this region. Epigenetic studies will also be conducted in Aspergillus infected and immunized mice that produce IL-17+ neutrophils, and we will use single cell RNA sequencing to characterize sub populations of IL-17+ neutrophils. Together, results of the proposed studies will identify the molecular events that underlie epigenetic regulation of IL-17 in neutrophils.